Desiccant-based air conditioning system

TECHNICAL FIELD

p-0002The present invention relates to a system for conditioning air.

BACKGROUND

p-0003Liquid desiccant air conditioning systems can provide an effective means to cool, dehumidify, and otherwise condition ambient air. Examples of such systems are described in the following international patent applications: WO 99/26026, WO 00/55546, and WO 03/056249.

p-0004One thing that is common to most desiccant-based air conditioning systems is the need to provide heating or cooling to control the temperatures of a fluids within the system—e.g., the desiccant on the dehumidification side, the desiccant on the regeneration side, and the airflows on either or both of these sides. Although the source of heating or cooling may come from any of a number of different sources, it would be advantageous to have a desiccant-based air conditioning system that could control the temperature of the desiccant by heat transfer to or from multiple sources, where each source could be used individually or together based on system needs and the availability of the sources.

SUMMARY

p-0005Embodiments of the invention include a system for conditioning air, where the temperature of a liquid desiccant is controlled using more than one or heat or cooling source in such a way that each of the sources can be used individually or combined depending on certain criteria.

p-0006In some embodiments, a heating capacity of an external heat source is evaluated. As used herein, the term “heating capacity” is a generic term that generally refers to an amount of heat available from the heat source. For example, if a water reservoir is heated by a solar energy source, and the volume of water in the reservoir is generally known, one measurement of the “heating capacity” would be to measure the temperature of the known volume of water. This would provide an indication of how much heat might be available from the heat source. In addition to a measurement of temperature for a known volume of material, the “heating capacity” may also be determined by any other method effective to convey an amount of heat available for use in the desiccant air conditioning system. For example, the type of material and its thermal conductivity may be taken into account to determine the heating capacity of the material, or other parameters may be used.

p-0007Once the heating capacity of the heat source is determined, and assuming for example that the desiccant on the regeneration side of the air conditioning system requires the addition of heat, it can then be determined whether the heating capacity is above a first predetermined amount. If, for example, the heating capacity is too low—i.e., it is below the first predetermined amount—heat transfer from the external heat source to the desiccant can be prohibited because such transfer would be inefficient, or in an extreme case, the desiccant may actually transfer heat back to the external heat source. If, however, the heating capacity is determined to be above the first predetermined amount, it may then be desirable to determine whether it is above a second predetermined amount.

p-0008If the heating capacity is determined to be above the second predetermined amount, which is higher than the first predetermined amount, then heat may be transferred exclusively from the external heat source to the desiccant, that is, heat is not transferred to the desiccant from any other heat source. Another type of heat source that may be used is the heat that is given off in a vapor-compression refrigeration cycle. In the example mentioned above, where the heating capacity of the external heat source is determined to be above the second predetermined amount, heat transfer from the refrigeration system to the desiccant may be prohibited. Conversely, if the heating capacity of the external source is determined to be above the first predetermined amount but below the second predetermined amount, it may be indicative that the external heat source has the capacity to provide some heat to the desiccant, but not all of the heat required. In such a case, heat may be transferred to the desiccant from both the external heat source and the other heat source, such as the refrigeration system.

p-0009Embodiments of the invention include a system for conditioning air that has a dehumidifier into which a first airflow is introduced and contacted with a liquid desiccant to transfer water from the first airflow to the liquid desiccant. A second airflow is introduced into a regenerator and contacted with liquid desiccant to transfer water from the liquid desiccant to the second airflow. The air conditioning system also includes a refrigeration system that has a plurality of heat exchangers, a refrigerant, and a compressor. Also included is a regeneration desiccant heat exchanger that is configured to selectively receive heat from the refrigeration system and selectively receive heat from an external heat source. The regeneration desiccant heat exchanger is also configured to receive the liquid desiccant from the regenerator to transfer heat from at least one of the refrigeration system or the external heat source to the liquid desiccant prior to the second airflow contacting the liquid desiccant.

p-0010In some embodiments, a first heat exchanger of the refrigeration system is configured to receive a heat transfer fluid, such as glycol, water and glycol, water, or any other fluid effective to transfer heat to the desiccant. The glycol receives heat from the refrigerant, and is selectively in contact with the regeneration desiccant heat exchanger for transferring heat to the liquid desiccant. A second heat transfer fluid is configured to receive heat from the external heat source, and selectively contact the regeneration desiccant heat exchanger to transfer heat to the liquid desiccant. The second heat transfer fluid may be, for example, hot water from a water reservoir heated by solar energy. Alternatively, the second heat transfer fluid could be glycol or a combination of glycol and water, or any other fluid effective to transfer heat from the external heat source to the regeneration desiccant heat exchanger. The external heat source, as noted above, can be solar energy; however, it may also be any other heat source effective to provide heat to the liquid desiccant. For example, the external heat source can be waste heat from an engine or other heat producing system, it can be geothermal energy, or heat from a cogeneration (CHP) system, just to name a few.

p-0011As discussed below, some embodiments of the present invention have the first and second heat transfer fluids enter the regeneration desiccant heat exchanger through a common inlet, such that they combine prior to entering the heat exchanger. In such cases, the first and second heat transfer fluids will have the same constituent materials, and may, for example, split their respective flows after leaving the heat exchanger, such that a portion goes back through the first refrigeration system heat exchanger, and another portion goes back to the external heat source.

p-0012Embodiments of the invention also include a second refrigeration system heat exchanger that is configured to receive a first coolant from an external cooling source, and to transfer heat from the refrigerant to the first coolant. This second refrigeration heat exchanger may be conveniently located upstream of the cool side of the refrigeration system, such that the very hot refrigerant receives a pre-cooling prior to entering an evaporator.

p-0013Some embodiments of the invention include an air conditioning system that includes a refrigeration system having a plurality of heat exchangers, a refrigerant, and a compressor. A dehumidifier receives a first airflow, where it contacts a liquid desiccant to transfer water from the first airflow to the liquid desiccant. A regenerator receives a second airflow where it contacts a liquid desiccant to transfer water from the liquid desiccant to the second airflow. The regenerator includes a first heat transfer loop for selectively transferring heat from the refrigeration system to the liquid desiccant prior to the second airflow contacting the liquid desiccant. It also includes a second heat transfer loop that selectively transfers heat from an external heat source to the liquid desiccant prior to the second airflow contacting the liquid desiccant.

p-0014The first heat transfer loop may include a regeneration desiccant heat exchanger configured to receive the liquid desiccant from the regenerator. It can also include a first of the refrigeration system heat exchangers that is configured to receive the refrigerant, and a first heat transfer fluid configured to selectively contact the first refrigeration system heat exchanger to receive heat from the refrigerant and to selectively contact the regeneration desiccant heat exchanger to transfer heat from the first heat transfer fluid to the liquid desiccant. The second heat transfer loop may include the regeneration desiccant heat exchanger, the external heat source, and a second heat transfer fluid configured to receive heat from the external heat source and to selectively contact the regeneration desiccant heat exchanger to transfer heat from the second heat transfer fluid to the liquid desiccant. The first and second heat transfer loops may be selectively combinable on an inlet side of the regeneration desiccant heat exchanger.

p-0015Embodiments of the invention also include a system for conditioning air that includes a dehumidifier into which a first airflow is introduced and contacted with a liquid desiccant to transfer water from the first airflow to the liquid desiccant. A second airflow is introduced into a regenerator and contacted with the liquid desiccant to transfer water from the liquid desiccant to the second airflow. A refrigeration system includes a plurality of heat exchangers, a refrigerant, and a compressor. A dehumidifier desiccant heat exchanger is configured to selectively transfer heat from the desiccant in the dehumidifier to the refrigeration system prior to the first airflow contacting the liquid desiccant. The dehumidifier desiccant heat exchanger is also configured to selectively transfer heat from the desiccant in the dehumidifier to an external cooling source prior to the first airflow contacting the liquid desiccant.

BRIEF DESCRIPTION OF THE DRAWINGS

p-0016<figref idrefs="DRAWINGS">FIG. 1</figref> is a schematic illustration of an air conditioning system in accordance with embodiments of the present invention; and

p-0017<figref idrefs="DRAWINGS">FIG. 2</figref> is a high-level flow chart illustrating embodiments of a control strategy for controlling the air conditioning system shown in <figref idrefs="DRAWINGS">FIG. 1</figref>; and

p-0018<figref idrefs="DRAWINGS">FIG. 3</figref> is a high-level flow chart illustrating embodiments of a control strategy for controlling the air conditioning system shown in <figref idrefs="DRAWINGS">FIG. 1</figref>.

DETAILED DESCRIPTION

p-0019<figref idrefs="DRAWINGS">FIG. 1</figref> shows an air conditioning system <b>10</b> in accordance with an embodiment of the present invention. In particular, the system <b>10</b> is configured to condition air—e.g., control the temperature and/or humidity of the air. In a broad sense, the air conditioning system <b>10</b> is broken down into two sections: a process side, or dehumidifier <b>12</b>, and a regenerator <b>14</b>. The air conditioning system <b>10</b> also includes a refrigeration system that is best described by its component parts. For example, the refrigeration system illustrated in <figref idrefs="DRAWINGS">FIG. 1</figref> includes heat exchangers <b>16</b>, <b>18</b>, <b>20</b>, <b>22</b> and <b>24</b>. The refrigeration system also includes a refrigerant, illustrated by the dashed line <b>26</b> on the hot side and by the dashed line <b>28</b> on the cold side of the refrigeration system. The refrigeration system also includes a receiver <b>30</b>, a filter <b>32</b>, a compressor <b>34</b>, an accumulator <b>36</b> and electric expansion valves <b>38</b>, <b>40</b>.

p-0020Although the air conditioning system <b>10</b> uses a vapor compression refrigeration system, the primary mechanism by which it conditions the air is through the use of a liquid desiccant <b>42</b>. In general, the desiccant <b>42</b> is pumped from a dehumidifier sump <b>44</b> by pump <b>46</b> through a filter <b>48</b> to the top of a matrix material <b>50</b>. The matrix <b>50</b> can be a sponge or other medium or media effective to facilitate contact between the desiccant <b>42</b> and a first airflow <b>52</b>. The airflow <b>52</b> is blown by a first blower <b>54</b>, which blows the first airflow <b>52</b> across the matrix <b>50</b> where water is absorbed from the first airflow <b>52</b> by the desiccant <b>42</b>. As the desiccant <b>42</b> flows downward through the matrix <b>50</b>, it becomes increasingly dilute, as it captures water from the airflow <b>52</b>. Without further processing, the desiccant <b>42</b> would become so dilute as to be ineffective at removing further water from the airflow <b>52</b>. Therefore, in the embodiment shown in <figref idrefs="DRAWINGS">FIG. 1</figref>, the dehumidifier sump <b>44</b> is connected to a regeneration sump <b>56</b> through an opening <b>58</b>.

p-0021In the regenerator <b>14</b>, the desiccant <b>42</b> is pumped by a pump <b>60</b> through a filter <b>62</b> to the top of matrix material <b>64</b> where it flows downward to contact a second airflow <b>66</b>, which is blown across the matrix <b>64</b> by a blower <b>68</b>. As the desiccant <b>42</b> flows through the matrix material <b>64</b>, it transfers water to the airflow <b>66</b> such that it becomes increasingly concentrated as it flows downward toward the regeneration sump <b>56</b>. The desiccant <b>42</b> may be transferred between the sumps <b>44</b>, <b>56</b> through the opening <b>58</b> by diffusion based on the concentration gradient between the desiccant in the dehumidifier <b>12</b> and the desiccant in the regenerator <b>14</b>. In addition, the desiccant <b>42</b> may be transferred between the dehumidifier <b>12</b> and the regenerator <b>14</b> through a float system <b>70</b> that includes two floats <b>72</b>, <b>74</b>, each of which has its own level switch <b>76</b>, <b>78</b>.

p-0022As shown in <figref idrefs="DRAWINGS">FIG. 1</figref>, desiccant <b>42</b> pumped by the dehumidifier pump <b>46</b> is split between the matrix <b>50</b> and the float <b>74</b>. Similarly, the desiccant <b>42</b> that is pumped by the regeneration pump <b>60</b> is split between the matrix <b>64</b> and the float <b>72</b>. Upon reaching a certain level within the float <b>72</b>, <b>74</b> the desiccant <b>42</b> is released to the opposite side of the air conditioning system <b>10</b> from which it came. As it is released, it travels through a heat exchanger <b>80</b> wherein heat is transferred from the warmer desiccant <b>42</b> on the regeneration side, to the cooler desiccant <b>42</b> from the dehumidifier side. A level switch <b>82</b> disposed in the dehumidifier sump <b>44</b> is also used to determine when the pump <b>46</b> should be activated to pump the desiccant <b>42</b> out of the dehumidifier sump <b>44</b>.

p-0023Liquid desiccants used in the present invention may be polycols, used alone or in mixture. Typical polycols include liquid compounds such as ethylene glycol, propylene glycol, butylene glycol, pentylene glycol, glycerol, trimethyol propane, diethytlene glycol, triethylene glycol, tetraethylene glycol, dipropylene glycol, tripropylene glycol, tetrapropylene glycol, and mixtures thereof. Polyol compounds which are normally solid, but which are substantially soluble in anhydrous liquid polyols or liquid hydroxyl amines, may also be used. Typical of these solid polyol compounds are erythritol, sorbitol, pentaerythritol and low molecular weight sugars. Typical hydroxyl amines include alkanolamines, such as monoethanol amine, diethanol amine, triethanol amine, isopropanol amine, including mono, di, and tri, isopropanol amine or digylcolamine.

p-0024Still other types of desiccants such as montmorillonite clay, silica gel, molecular sieves, CaO, CaSO4 can all be used. As would be evident to persons of ordinary skill in the art, the selection of a desirable desiccant depends, among other parameters, upon the temperature and humidity ranges of ambient air from which moisture is to be absorbed. Still other exemplary desiccants comprise materials such as P2O5, BaO, Al2O3, NaOH sticks, KOH fused, CaBr2, ZnCl2, Ba(ClO4)2, ZnBr2. The desiccant <b>42</b> shown in <figref idrefs="DRAWINGS">FIG. 1</figref> may advantageously comprise an aqueous solution of approximately 40% lithium chloride.

p-0025To increase the efficiency of the air conditioning system <b>10</b>, the desiccant <b>42</b> on the dehumidifier side <b>12</b> may be selectively cooled, while the desiccant <b>42</b> on the regenerator side <b>14</b> may be selectively heated. On the regeneration side <b>14</b> is a regeneration desiccant heat exchanger <b>84</b>. The heat exchanger <b>84</b> is configured to selectively receive heat from the refrigeration system, for example, through a first heat transfer fluid <b>86</b> that receives heat from the refrigerant <b>26</b> in a first of the refrigeration system heat exchangers <b>16</b>. As discussed above, the heat transfer fluid <b>86</b> can be a liquid, such as a mixture of glycol and water, or any medium effective to transfer heat. The heat exchanger <b>84</b> is also configured to selectively receive heat from an external heat source <b>88</b>, such as a liquid reservoir heated by solar energy, a geothermal heat source, etc.

p-0026A second heat transfer fluid indicated by the long dashed line <b>90</b> can flow directly to an inlet <b>95</b> of the heat exchanger <b>84</b>. In particular, valves <b>92</b>, <b>94</b> can control the flow of the heat transfer fluid <b>90</b> to and from the heat exchanger <b>84</b>. Similarly, a valve <b>96</b> can control the flow of the heat transfer fluid <b>86</b> to and from the heat exchangers <b>16</b>, <b>84</b>. A pump <b>98</b> is used to pump the heat transfer fluid <b>86</b> through the refrigeration heat exchanger <b>16</b> and the regeneration desiccant heat exchanger <b>84</b>. Another pump or pumps (not shown) can be used to pump the heat transfer fluid <b>90</b> to and from the external heat source <b>88</b> and through the inlet <b>95</b> and outlet <b>99</b> of heat exchanger <b>84</b>.

p-0027As shown in <figref idrefs="DRAWINGS">FIG. 1</figref>, the flow of the first heat transfer fluid <b>86</b> defines a first heat transfer loop that includes the heat exchangers <b>16</b>, <b>84</b>. Similarly, the heat transfer fluid <b>90</b> defines a second heat transfer loop that includes the heat exchanger <b>84</b> and the external heat source <b>88</b>. By having two different heat sources that can directly transfer heat to the desiccant <b>42</b>, the air conditioning system <b>10</b> may provide greater efficiencies over systems that use a single heat source to heat the desiccant. Each of the heat transfer fluids <b>86</b>, <b>90</b> can enter the heat exchanger <b>84</b> through a common inlet <b>95</b>, and therefore, may have the same constituent materials—e.g., water, glycol, etc.

p-0028Turning to <figref idrefs="DRAWINGS">FIG. 2</figref>, a flow chart <b>100</b> is shown, which illustrates a control system for controlling the heat supplied to the desiccant <b>42</b> on the regeneration side <b>14</b> as illustrated in <figref idrefs="DRAWINGS">FIG. 1</figref>. At the first step <b>101</b>, it is determined that heating is required. This may be determined, for example, by measuring the conditions of the supply air or the return air to determine that increased dehumidification is required. Once this determination is made, the method moves to step <b>102</b>, where the heating capacity of the external heat source <b>88</b> is determined. As discussed above, there may be any number of ways to determine the heating capacity of the external heat source <b>88</b>, such as determining a temperature and volume of a reservoir of liquid. In general, a control strategy is then implemented to determine whether to transfer heat from the external source <b>88</b> to the desiccant <b>42</b> in the regenerator <b>14</b>, and if so, whether some or all of the heat will come from the external source <b>88</b>.

p-0029If it is determined that its heating capacity is great enough, at least some of the heat transferred to the desiccant <b>42</b> in the regenerator <b>14</b> will come from the external heat source <b>88</b>. A high-level diagram of such a control system is illustrated in the flow chart <b>100</b>. Such a control system may reside in one or more hardware controllers, software controllers, or a combination of hardware and software controllers. The control system can receive inputs from various sensors as described below, and can control various elements of the system <b>10</b>, such as pumps and valves, to achieve the desired control strategy. Such a control system <b>103</b> is illustrated schematically in <figref idrefs="DRAWINGS">FIG. 1</figref>.

p-0030Returning to <figref idrefs="DRAWINGS">FIG. 2</figref>, a determination is made at decision block <b>104</b> as to whether the heating capacity determined at step <b>102</b> is above a first predetermined amount. If it is not, heat is transferred from the refrigeration system, for example, by opening valve <b>96</b>—see step <b>106</b>. In addition, heat transfer from the external source <b>88</b> to the desiccant <b>42</b> may be prohibited, for example, by closing the valves <b>92</b>, <b>94</b> to shut off the flow of the heat transfer fluid <b>90</b> to and from the heat exchanger <b>84</b>.

p-0031If it is found that the heating capacity of the external heat source <b>88</b> is above the first predetermined amount, then at least some of the heat transferred to the desiccant <b>42</b> in the heat exchanger <b>84</b> may come from the external heat source <b>88</b>. Whether only a portion of the heat transferred to the desiccant <b>42</b> comes from the external heat source <b>88</b>, or whether all of it is from the external heat source <b>88</b> depends on how far above the first predetermined amount the heating capacity of the external heat source <b>88</b> is. For example, it is determined at decision block <b>108</b> whether the heating capacity of the external heat source <b>88</b> is above a second predetermined amount, which is above the first predetermined amount. If the answer is “yes”, then all of the heat to be transferred to the desiccant <b>42</b> in the heat exchanger <b>84</b> will come from the external heat source <b>88</b>, and transfer of heat from the refrigeration system through heat exchanger <b>16</b>, is prohibited. This may be accomplished by shutting off the pump <b>98</b> and closing the valve <b>96</b>—see step <b>110</b>.

p-0032If the heating capacity of the external heat source <b>88</b> is between the first and second predetermined amounts, then heat will be transferred to the desiccant <b>42</b> in the heat exchanger <b>84</b> from both the external heat source <b>88</b>, and the refrigeration system—see step <b>112</b>. In at least some embodiments of the invention, the external heat source <b>88</b> will be used to the full extent of its capacity to provide as much heat as possible; the refrigeration system will be used to provide only that portion of heat not available from the external heat source <b>88</b>. This reduces the reliance on the refrigeration system, which will generally result in less energy being used and a lower cost of operation. Stated another way, the flow of the heat transfer fluid <b>90</b> is controlled to provide a maximum amount of heat from the external heat source <b>88</b>, and the flow of the heat transfer fluid <b>86</b> is controlled to provide a minimum amount of heat from the refrigeration system.

p-0033The actual values of the first and second predetermined amounts used to evaluate how heat will be transferred to the desiccant <b>42</b> may depend on a number of factors, including the temperature of the desiccant <b>42</b>, and the state of the conditioned air <b>114</b> as it leaves the dehumidifier <b>12</b>. In order to effectively control the temperature and humidity of the conditioned air <b>114</b>, the air conditioning system <b>10</b> relies on a number of different sensors configured to measure certain system parameters. For example, temperature sensors designated “T”, pressure sensors designated “PT”, and temperature/relative humidity sensors designated “T,Rh” are shown in various locations throughout the system <b>10</b>. These sensors measure the relevant parameter, and then transmit signals to a control system which, for example, can implement various control methods, such as the method illustrated in the flow chart <b>100</b> in <figref idrefs="DRAWINGS">FIG. 2</figref>.

p-0034As discussed above, the heat exchanger <b>84</b> can receive hot fluid from one or both of the refrigeration system and the external heat source <b>88</b>. The valves <b>92</b>, <b>94</b>, <b>96</b> are used to control the flow of the heat transfer fluids <b>86</b>, <b>90</b>, and such control may be as described above with regard to the method illustrated in <figref idrefs="DRAWINGS">FIG. 2</figref>. To provide additional efficiencies in the air conditioning system <b>10</b>, the refrigerant <b>26</b> can be routed through the heat exchanger <b>20</b>, which is configured to heat the airflow <b>66</b> prior to its contacting the desiccant <b>42</b> in the matrix <b>64</b>. In this way, the airflow <b>66</b> can absorb more of the water from the desiccant <b>42</b> in the regenerator to increase the concentration of the desiccant <b>42</b> in the regeneration sump <b>56</b>. Thus, the airflow <b>116</b> is warm and water-laden. To the extent that the air conditioning system <b>10</b> is used to condition the air for a living space, such that control of the temperature and humidity of the airflow <b>114</b> is the ultimate goal, the airflow <b>116</b> may be waste air. Conversely, if the air conditioning system <b>10</b> is utilized in a water capture and treatment application, the airflow <b>114</b> may be the waste air, while the airflow <b>116</b> is cooled or otherwise treated to remove the water for drinking or other applications.

p-0035Just as the regenerator <b>14</b> can utilize an external heat source, such as the heat source <b>88</b>, the dehumidifier <b>12</b> can utilize an external cooling source <b>118</b>. The external cooling source <b>118</b> may be, for example, a source of cool water from a ground well, surface water, or a cooling tower, just to name a few. As shown in <figref idrefs="DRAWINGS">FIG. 1</figref>, a coolant <b>120</b>, which may be water, glycol, a mixture of the two, or some other fluid, flows through one of the refrigeration system heat exchangers <b>18</b>, and back to the external cooling source <b>118</b>. This flow can be controlled, for example, by valves <b>122</b>, <b>124</b>. Although the valve <b>122</b> is illustrated in <figref idrefs="DRAWINGS">FIG. 1</figref> as a manual valve, and the valve <b>124</b> is illustrated as an electric solenoid, other types of valves can be used in such a system.

p-0036Another portion of the coolant <b>120</b> flows through a first heat exchanger <b>126</b> in the dehumidifier <b>12</b>. Upon exiting the heat exchanger <b>126</b> it flows back to the external cooling source <b>118</b>, the flow of which is controlled by an electric solenoid valve <b>128</b>. In addition to the heat exchanger <b>126</b>, and one of the refrigeration system heat exchangers <b>22</b>, the dehumidifier also includes a dehumidifier desiccant heat exchanger <b>130</b>. The heat exchanger <b>130</b> receives the desiccant <b>42</b> from the dehumidifier sump <b>44</b> as it is pumped by the pump <b>46</b>. One or both of the refrigeration system or the external cooling source <b>118</b> can provide cooling to the desiccant <b>42</b> through the dehumidifier desiccant heat exchanger <b>130</b>. For example, when the solenoid valve <b>128</b> is open, some of the coolant <b>120</b> flows through the heat exchanger <b>126</b>, where it receives heat from a second coolant <b>132</b>. The coolant <b>132</b> then flows through one of the refrigeration system heat exchangers <b>22</b> where it is further cooled by the refrigerant <b>28</b>. Thus, when the coolant <b>132</b> reaches the heat exchanger <b>130</b>, it has been cooled by both cooling sources and can remove a greater quantity of heat from the desiccant <b>42</b> in the dehumidifier <b>12</b>. To the extent that the external cooling source cannot provide adequate cooling, or is not required, the solenoid valve <b>128</b> can be closed so that the coolant <b>132</b> is cooled only by the refrigerant <b>28</b> in the heat exchanger <b>22</b>. To the extent that the desiccant <b>42</b> does not require cooling, the coolant pump <b>134</b> can be shut off.

p-0037Similar to the control of desiccant heating in the regenerator <b>14</b>, control of desiccant cooling in the dehumidifier <b>12</b> can be controlled through a control system that receives multiple sensor inputs indicating various temperatures, pressures, and humidities and determines the appropriate source and quantity for cooling the desiccant <b>42</b> in the dehumidifier <b>12</b>. Additional control and conditioning of the airflow <b>114</b> leaving the dehumidifier <b>12</b> can be obtained by using the heat exchanger <b>24</b>, which is another evaporator within the refrigeration system. In this way, the temperature and humidity of the airflow <b>114</b> can be effectively and efficiently controlled using the air conditioning system <b>10</b> to provide a desired output.

p-0038<figref idrefs="DRAWINGS">FIG. 3</figref> shows a flow chart <b>136</b>, which illustrates a method of controlling the cooling of the desiccant <b>42</b> in the dehumidifier <b>12</b> as illustrated in <figref idrefs="DRAWINGS">FIG. 1</figref>. At the first step <b>138</b>, it is determined that cooling is required. This may be determined, for example, by measuring the conditions of the supply air—such as temperature and/or humidity—and comparing these conditions to the set point. The set point is the value or values of desired conditions as chosen by a user of the system <b>10</b>, and may include, for example, one or both of a desired temperature and humidity. Once this determination is made, the method moves to step <b>140</b>, where the cooling capacity of the external cooling source <b>118</b> is determined. Just like the heating capacity of a heating source as discussed above, there may be any number of ways to determine the cooling capacity of the external cooling source <b>88</b>, such as determining a temperature and volume of a reservoir of liquid. In general, a control strategy is then implemented to determine whether to provide cooling from the external source <b>118</b> to the desiccant <b>42</b> in the dehumidifier <b>12</b>, and if so, whether some or all of the cooling will come from the external source <b>118</b>.

p-0039If it is determined that the cooling capacity of is great enough, at least some of the cooling provided to the desiccant <b>42</b> in the dehumidifier <b>12</b> will come from the external cooling source <b>118</b>. A high-level diagram of such a control system is illustrated in the flow chart <b>136</b>, where a determination is made at decision block <b>142</b> as to whether the determined cooling capacity is above a first predetermined amount. If it is not, cooling is provided by the refrigeration system, for example, by operating pump <b>134</b> and by closing the valve <b>128</b> to shut off the flow of the coolant <b>120</b> to and from the heat exchanger <b>126</b>—see step <b>144</b>. In such a case, all of the heat transferred from the desiccant <b>42</b> in the heat exchanger <b>130</b> will be transferred to the refrigerant <b>28</b> of the refrigeration system.

p-0040If it is found that the cooling capacity of the external cooling source <b>118</b> is above the first predetermined amount, then at least some of the cooling provided to the desiccant <b>42</b> in the heat exchanger <b>130</b> may come from the external cooling source <b>118</b>. Whether only a portion of the cooling provided to the desiccant <b>42</b> comes from the external cooling source <b>118</b>, or whether all of it is from the external cooling source <b>118</b> depends on how far above the first predetermined amount the cooling capacity of the external cooling source <b>118</b> is. For example, it is determined at decision block <b>146</b> whether the cooling capacity of the external cooling source <b>118</b> is above a second predetermined amount, which is above the first predetermined amount. If the answer is “yes”, then all of the cooling provided to the desiccant <b>42</b> in the heat exchanger <b>130</b> will come from the external cooling source <b>118</b>, and cooling provided from the refrigeration system through heat exchanger <b>22</b> is prohibited. This may be accomplished, for example, by closing the valve <b>38</b>—see step <b>148</b>.

p-0041If the cooling capacity of the external cooling source <b>118</b> is between the first and second predetermined amounts, then cooling will be provided to the desiccant <b>42</b> in the heat exchanger <b>130</b> from both the external cooling source <b>118</b>, and the refrigeration system—see step <b>150</b>. In at least some embodiments of the invention, the external cooling source <b>118</b> will be used to the full extent of its capacity to provide as much cooling as possible; the refrigeration system will be used to provide only that portion of cooling not available from the external cooling source <b>118</b>. This reduces the reliance on the refrigeration system, which will generally result in less energy being used and a lower cost of operation.

p-0042Similar to the control strategy used on the regeneration side, the control strategy illustrated in <figref idrefs="DRAWINGS">FIG. 3</figref> controls the flow of the refrigerant <b>28</b> through the heat exchanger <b>22</b> and the flow of the coolant <b>120</b> through the heat exchanger <b>126</b> to maximize the amount of heat transferred from the coolant <b>132</b> to the coolant <b>120</b>, and to minimize the amount of heat transferred from the coolant <b>132</b> to the refrigerant <b>28</b>. As with the heating capacities described above, the actual values of the first and second predetermined amounts used to evaluate how cooling will be provided to the desiccant <b>42</b> may depend on a number of factors, including the temperature of the desiccant <b>42</b> on the process side, and the state of the conditioned air <b>114</b> as it leaves the dehumidifier <b>12</b>.

p-0043While exemplary embodiments are described above, it is not intended that these embodiments describe all possible forms of the invention. Rather, the words used in the specification are words of description rather than limitation, and various changes may be made without departing from the spirit and scope of the invention. Additionally, the features of various implementing embodiments may be combined to form further embodiments of the invention.